Gas in the water

Image of the month - August 2002

CO2 transfer velocity between the atmosphere and ocean for February (top) and September (below) (temperature-related effects have been removed). Absorption of CO2 by the ocean is faster in winter (Northern or Southern). (Credits WHOI).

One of the major unknowns in modeling climate variations is the estimated CO2 content in the atmosphere and absorption of CO2 by the ocean. Here again, satellite altimetry can help. This time it is not measurements of actual sea surface height that interest us, but what the received radar signal can tell us about surface reflectivity. CO2 absorption increases with sea surface roughness. A rough sea surface also causes reflected radar waves to scatter more, meaning that the return signal received by the altimeter is weaker.
Sea surface conditions depend on wind and on many other factors, such as the presence of a surfactant film. CO2 absorption varies seasonally.



CO2 velocity transfer varies with latitude (a). It is very low at the Equator, slightly higher in the Tropics, and higher at latitudes above 30° in the Southern Hemisphere than in the Northern Hemisphere (where there are more continental land masses).
It also varies from one year to another (b).
(Credits WHOI)